What Is Color Management, And Why Should I Care About It?

The term "color management" denotes the process of standardizing the relationship between the numeric data in digital image files and the colors output from monitors and printers, or measured by scanners and digital cameras. Using numbers to describe and record color values is useless without some kind of standardized method of correlating those numbers to actual colors. This is one of the most fundamental aspects of digital photography and imaging, but is also the most confusing and frustrating and misunderstood. Good color management practices enable one to capture digital images, view them on a monitor, and print them with the colors of the image captured, displayed, and printed in a consistent, accurate and repeatable manner. A properly color managed workflow (the process that lies between pressing the shutter button and removing the print from the printer) can be difficult to set up, but the dividends reaped in time saved, less waste of paper and ink, and general frustration can be enormous.

Color Management, Color Spaces, And Profiles

One of the most important concepts in color management is the profile. A profile can be thought of as a very detailed description of the relationship between device color numbers and real-world colors for a scanner, camera, monitor, or printer. A profile also describes the gamut of a device, the range of colors the device is capable of capturing, displaying, or printing. The boundaries of a device's gamut surround what is referred to as the device's color space. There are also some commonly used color spaces that do not actually correspond to any physical device, but are mathematical abstractions used for image editing. Common editing spaces include sRGB, Apple's ColorMatch, and Adobe RGB 1998. On thing all these spaces have in common is that equal RGB values will be a neutral gray: an RGB value of 45,45,45 is a dark gray, and 220,220,220 is a light gray. Device-specific color spaces do not have this property, color values that correspond to a neutral gray are typically unequal, like 210,225,207. For this reason, editing an image in a standard working space is greatly preferable; if a pixel colored 203,203,203 has a color cast, you know that it should display and print as a neutral gray and you have a profile problem.

Every color device has its own unique color space and gamut. No two printers, scanners, cameras, or monitors display colors exactly the same way. Even if they are the same brand, model, and lot number, there will still be minor differences in the way they record or display colors. Monitors are especially troublesome in this regard; in addition to the significant unit-to-unit variations present at the time of manufacture, their color performance will change significantly over time as the phosphors in the picture tube or the LCD backlight lamp(s) age. Over time, the overall brightness of the monitor will decrease, and the range of colors that it can display will gradually shrink. Printers tend to be more well-behaved in this regard; the main cause of print color changes over time is variations between different lots of ink or toner used. Cameras tend to be the most well-behaved color devices, both in unit-to-unit consistency and in the consistent performance of a unit over time. Scanners vary, models that use LEDs to illuminate the film or paper will be much more consistent than models that use fluorescent lamps, which contain phosphors that degrade with age.

Profiles bring order to the chaos of device color performance. By accurately documenting the relationship between device color numbers and standard colors, it becomes possible to capture, display, and print colors consistently using devices from many different manufacturers. If you want to print a certain shade of green, the printer profile will tell you what color numbers to send to the printer to get that shade of green. A monitor profile will tell you what color numbers to send to the monitor to make it display that shade of green. Color managed applications like Adobe Photoshop utilize monitor and printer profiles to ensure that monitor and print colors match. But the important thing to remember is that the quality and accuracy of the profiles is critical. Monitor-to-print matching can only be as good as the monitor and printer profiles and the ability of your monitor and printer to consistently match them. Lighting conditions are also a factor, but that will be dealt with in more detail later.

Gamma

Gamma is a term used to describe how a color space defines the luminance (brightness) transition from black to white. A gamma value of 1.0 would indicate a linear relationship between luminance and the numeric values used to describe it. Doubling the luminance values would double the measured brightness value of the color. This would seem to be the logical choice, but it is actually almost never used. The reason for this is that the way human vision perceives luminance is not linear, it is logarithmic. If you were to view 3 light bulbs that were emitting 100, 200, and 400 lumens of light, the brightness difference between bulbs 1 and 2 would appear to be of the same magnitude as the brightness difference between bulbs 2 and 3, even though there is a 100 lumen difference between bulbs 1 and a 200 lumen difference between bulbs 2 and 3. The practical result of all this is that a color space with a gamma of 1.0 would be able to describe shadows and dark colors with a much greater degree of precision than light colors and highlights. Most of the possible numeric values would describe dark colors, and very few would describe light colors.

Most commonly used editing spaces, such as sRGB and Adobe RGB 1998, use a gamma of 2.2, since that value closely corresponds to the luminance response of human vision. The only major exceptions to this are Apple's ColorMatch space and ProPhoto, which use a gamma of 1.8. This is a holdover from some of Apple's older-model black & white monitors which were built with a native gamma of 1.8. However, almost all monitors manufactured today (even those manufactured by Apple) have a native gamma between 2.0 and 2.4. This means that image files edited in a gamma 1.8 space will appear too dark on more than 90% of monitors, unless the viewer has a 100% color managed viewing setup.

Monitor Profiling

A properly profiled monitor is absolutely critical to creating good quality digital images. Your monitor is what brings the abstract, non-physical color numbers in a digital image to life in a form that can be perceived by your sense of sight. You must be able to rely on the accuracy of your monitor's display; it is the only way you have to see your image as you are editing and adjusting it. If it does not faithfully and accurately display the color numbers in your image file, any effort to correct or adjust the colors in your image file is doomed from the start.

The only way to properly profile your monitor is to measure the color output with a device that attaches to the display screen. There are 2 basic types of monitor calibrators; the colorimeter and the more accurate (but much more expensive) spectrophotometer. Both of these devices work similarly: they are attached to the monitor screen, and an accompanying software program is run, which displays a series of color test patterns onscreen. The light output from the test pattern on the monitor screen is measured by the device, and the measurements are used to build the monitor profile. The profile is saved on your computer, and is set to be your default display profile. This allows Photoshop and other color-savvy applications to find the monitor profile and use it. There are monitor profiling applications out there (most notably Adobe Gamma) that purport to profile your monitor without attaching a hardware device to it. These are slightly better than nothing, in the same sense that putting a band-aid on a black widow spider bite is slightly better than nothing, but getting proper medical treatment is vastly preferable. Unless you are on a really austere budget, don't waste your time--get a real solution. The Colorvision Spyder works well, as does the Gretag-Macbeth i1.

Printer Profiling

A good printer profile is nearly as important as a good monitor profile. I say "nearly" because if you properly edit your file in a standard editing space, like Adobe RGB 1998, you can send that image to a lab with good color management and get a good print the first time without worrying about a printer profile yourself. Of course, the lab has to have a good printer profile for that to happen, but that's their problem, not necessarily yours. If you make your own prints, be aware that most printers come with profiles created by the manufacturer. The quality of these profiles varies widely, and their usefulness is completely dependent on how closely the color performance of your printer matches the unit(s) the manufacturer used to make the profile. Better quality printers, like those from Canon and Epson, have driver settings that allow you to ignore the factory profiles and create your own.

To profile a printer, you print out a test chart with all printer profiles and driver color adjustments disabled, and measure the colors of the test chart with a spectrophotometer. Since spectrophotometers are expensive ($500-$4000), and measuring the test charts can be tricky, there are many places that offer profiling services. You download their test chart, print it according to the instructions, and mail them the test chart and a check. They measure the chart, build the profile, and email it back to you. Prices typically range between $50 and $100 per profile. A printer profile is only good for one specific type of paper; if you print on Epson Enhanced Matte and Canon Photo Paper Pro, you will need a separate profile for each paper. And if you have multiple printers, each one should be profiled separately.

Camera Profiling

Camera profiling is the least important part of a color managed workflow, but the issue shouldn't be ignored. It is least important because the output from a camera is typically adjusted and tweaked to compensate for the wide variety of lighting conditions encountered while photographing, and it is common to make color adjustments for aesthetic or artistic reasons that have little to do with "keeping it real". For example, it is common to adjust Caucasian skin tones in portraits to a slightly warmer tone than strict color fidelity would dictate. And other people have a flushed complexion that tends to make them look like an alcoholic without a little help from Photoshop. Landscape images typically have color saturation increased, and contrast adjustments made to increase their visual impact. A good camera profile can reduce the amount of color correction needed in any kind of photographic work, but it is of the greatest value when printing images "as shot" without any tweaking is desired, or in certain types of product or fashion work where an exact color match between the camera image and the original product is required.

Creating a profile for a camera requires photographing a special test chart under carefully controlled exposure and lighting conditions, and is not an undertaking for the non-expert. There are places that offer camera profiling services, but you have to send them your camera and several hundred dollars. It's not something to be undertaken lightly if you have an expensive camera, and for a working pro, being without the camera for days or weeks can be even more costly than the profiling fee. And then there's the risk of loss or damage during shipping to and from the profiling service.

Camera profiles are most easily used when converting RAW image files (which contain the unprocessed data from the camera sensor) to a standard image file. Phase One's Capture One is the only RAW converter that currently supports external camera profiles; it comes with a selection of pre-made profiles for a variety of cameras, and also supports profiles made by third parties.

Adobe Camera RAW has a kinda-sorta profile feature built-in; it has a page of calibration adjustments that allow you to modify the behavior of its internal built-in profiles. It's not technically profiling, but it is a way to customize the color processing for your camera, and it works quite well. This feature can also be used to match the color characteristics of multiple cameras. Tom Fors has a very useful ACR Calibrator Script that automates calculating the optimum calibration settings from a properly-exposed and illuminated RAW image of a Gretag-Macbeth Color Checker. See Camera Profiling for more details.

JPEG images generated in-camera can also be profiled, but the profile must be assigned to the image file either manually or with a Photoshop action; this is not something that can be done in-camera.

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